1. Field of the Invention
The present invention relates to a method and apparatus for inspecting a communicating hole of a cast molded article for inspecting the degree of obstruction of a communicating hole formed in a cast molded article, and more particularly relates to a method and apparatus for inspecting a communicating hole of a cast molded article suitable for inspecting the degree of obstruction of a communicating hole for cooling water formed within a cast molded article such as a cylinder block of an engine.
2. Description of the Related Art
A cast molded article such as a cylinder block or a cylinder head of an automobile is provided with a network of communicating holes therein for cooling water. These communicating holes are formed by arranging a core within a mold. However, there are cases in which heat and the flow of molten metal during cast molding cause the core to crack and break, obstructing the communicating hole and making it narrow. Since this type of defect may lead to poor cooling, poor engine efficiency, and seizure of the engine, it is necessary to inspect the communicating holes of all products after cast-molding. However, because the communicating holes of which there is a complex network inside cast molded articles twist and bend, they can not be directly visually checked for defects as can be linear communicating holes.
Therefore, the quality of communicating holes is determined using various means such as by manually shining a light into the opening of a communicating hole and looking at the reflected light that passes through to the other end, or by passing a wire or the like through the communicating hole. The quality of complex communicating holes is determined using such means as an endoscopic light source capable of bending at the end or observing the inside with optic fiber. However, with the method of passing a wire through the communicating hole it was difficult not only to pass the wire through a communicating hole, but also to know just how narrow the communicating hole was. Moreover, the operation was troublesome. Also, an endoscope and optic fiber were not able to be inserted all the way into the inner portion of complex communicating holes and much manual labor was required.
In an attempt to automate inspection, investigations have also been made into detecting light illuminated into a communicating hole from an opening thereof with an optical sensor disposed at an adjoining communicating hole opening, as well as feeding air into a communicating hole from an opening thereof and detecting the air pressure and air flow rate at an adjoining communicating hole opening. However, because the inside of a communicating hole changes color and its surface becomes rough, light passed through a communicating hole attenuates to {fraction (1/100)} or less, so that sufficient determination can not be made. Also, with the air method, due to the fact that air leaks from other communicating holes that branch off, the air pressure attenuates to {fraction (1/1000)} or less at the branching point, so that sufficient determination can not be made. Therefore, practical application of either of these methods was difficult. In addition, it is necessary to fit the air feed hole and pressure sensor tightly against the communicating hole opening during measuring so air does not leak, as well as have the light source and light sensor as close as possible to the communicating hole opening in order to inhibit attenuation. These make setup prior to measuring troublesome and time consuming.
The object of the present invention is to provide a method and apparatus for inspecting a communicating hole of a cast molded article which enables reliable determination of the quality of a communicating hole of a complex shape formed in a cast molded article.
A first aspect of the present invention is a method of inspecting a communicating hole of a cast molded article, in which audible sound waves are emitted into one end of a communicating hole of a cast molded article and the audible sound waves which passed through the communicating hole are received at the other end thereof. The frequency spectrum of the received audible sound waves are then computed and processed based on a reference frequency spectrum, such that the quality of the communicating hole is determined.
Also, a second aspect of the present invention is an apparatus for inspecting a communicating hole of a cast molded article, provided with an audible sound wave transmitter disposed at one end of the communicating hole of a cast molded article, an audible sound wave receiver disposed at the other end of the communicating hole for receiving the audible sound waves sent from the transmitter which has passed through the communicating hole, and a computing and processing device for determining the quality of the communicating hole by computing and processing the frequency spectrum of the audible sound waves received by this receiver based on a reference frequency spectrum.
Further, in the first and second aspects above, the audible sound waves from the transmitter are able to be swept from a low frequency to a high frequency or from a high frequency to a low frequency. It is preferable to use audible sound waves of a frequency of 1 to 20,000 Hz. A plurality of transmitters and/or receivers may be provided.
Moreover, the above-mentioned computing and processing in the first and second aspects enables the frequency spectrum of the received audible sound waves to be computed and processed by a neural network.